During reactor startup, critical rod position is affected by:
A. core flow rate.
B. source range initial count rate.
C. recirculation ratio.
D. fuel burnup.
ANSWER: D.
Comment: The question is unsatisfactory because it indicates that fuel burnup is occurring during startup. The critical rod position for a reactor startup depends on the fuel burnup.
QID: B1065 (N/A) (TOPIC: 292008 KNOWLEDGE: K1.02 [3.8/3.8])
A refueling outage has just been completed and a reactor startup is being commenced. Which one of the following lists the method(s) used to add positive reactivity during the startup to criticality?
A. Control rods only
B. Recirculation pump flow only
C. Control rods and recirculation pump flow
D. Recirculation pump flow and steaming rate
ANSWER: A.
Comment: The question is technically incorrect because "reactivity" is not added. See B2048 in the section on Neutron Life Cycle for a discussion of reactivity and reactivity change.
QID: B266 (P65) (TOPIC: 292008 KNOWLEDGE: K1.03 [4.1/4.0])
While withdrawing control rods during a reactor startup, the count rate doubles. If the same amount of reactivity that caused the first doubling is added again, the count rate will __________ and the reactor will be ____________.
A. more than double; subcritical
B. more than double; critical
C. double; subcritical
D. double; critical
ANSWER: B.
Comment: This question suffers the same defect as B1065. In addition, a BWR startup does not introduce "equal" reactivity increments; power doubling is employed which results in a sequence of progressively smaller reactivity increments. The question does not pose an "operational" situation and can be misleading.
QID: B1565 (P1065) (TOPIC: 292008 KNOWLEDGE: K1.03 [4.1/4.0])
During a reactor startup, equal increments of positive reactivity are being sequentially added and the count rate is allowed to reach equilibrium after each addition. Which one of the following statements concerning the equilibrium count rate applies after each successive reactivity addition?
A. The time required to reach equilibrium count rate is the same.
B. The time required to reach equilibrium count rate is shorter.
C. The numerical change in equilibrium count rate increases.
D. The numerical change in equilibrium count rate is the same.
ANSWER: C.
Comment: The question suffers the same defect as B266. Reactivity is not added and the question is not operational.
QID: B1964 (TOPIC: 292008 KNOWLEDGE: K1.03 [4.1/4.0])
A reactor startup is in progress and the reactor is slightly subcritical. Assuming the reactor remains subcritical, a short control rod withdrawal will cause the reactor period to initially shorten, and then:
A. gradually lengthen and stabilize at a negative 80 second period.
B. gradually lengthen and stabilize at infinity.
C. gradually lengthen until reactor power reaches the point of adding heat, then stabilize at infinity.
D. gradually lengthen until the neutron population reaches equilibrium, then stabilize at a negative 80 second period.
ANSWER: B.
Comment: The question is technically incorrect because units are not specified for reactor period. The period will stabilize at infinite seconds. It is always good practice to assign units, where applicable.
QID: B2165 (P1766) (TOPIC: 292008 KNOWLEDGE: K1.03 [4.1/4.0])
A reactor startup is in progress with the reactor currently subcritical. Which one of the following describes the change in count rate resulting from a short control rod withdrawal with Keff at 0.95 as compared to an identical control rod withdrawal with Keff at 0.99? (Assume reactivity additions are equal, and the reactor remains subcritical.)
A. Both the prompt jump in count rate and the increase in stable count rate will be the same.
B. Both the prompt jump in count rate and the increase in stable count rate will be smaller with Keff at 0.95.
C. The prompt jump in count rate will be smaller with Keff at 0.95, but the increase in stable count rate will be the same.
D. The prompt jump in count rate will be the same, but the increase in stable count rate will be smaller with Keff at 0.95.
ANSWER: B.
Comment: The question suffers the same defect as B1065. Reactivity is not added. In addition, the terminology is poor. The final count rate is a condition of "equilibrium source multiplication."
QID: B2465 (P2466) (TOPIC: 292008 KNOWLEDGE: K1.03 [4.1/4.0])
A reactor startup is being performed by adding equal amounts of positive reactivity and waiting for neutron population to stabilize. As the reactor approaches criticality, the numerical change in stable neutron population after each reactivity addition __________, and the time required for the neutron population to stabilize after each reactivity addition ___________.
A. increases; remains the same
B. increases; increases
C. remains the same; remains the same
D. remains the same; increases
ANSWER: B.
Comment: The question suffers the same defect as B266. Reactivity is not added and the question is not operational.
QID: B67 (TOPIC: 292008 KNOWLEDGE: K1.04 [3.3/3.4])
As a reactor approaches criticality during a reactor startup it takes longer to reach an equilibrium neutron count rate after each control rod withdrawal due to the increased:
A. fraction of fission neutrons leaking from the core.
B. number of neutron generations required to reach a stable level.
C. length of time from neutron generation to absorption.
D. fraction of delayed neutrons appearing as criticality is approached.
ANSWER: B.
Comment: The question is technically incorrect because "neutron generations" are a fictitious entity associated with the primitive life cycle model, which cannot accurately describe actual reactor behavior. The explanation should be based on the one-delay group model.
QID: B365 (P365) (TOPIC: 292008 KNOWLEDGE: K1.04 [3.3/3.4])
Which one of the following statements describes count rate characteristics after a 5 second control rod withdrawal with the reactor very close to criticality? (Assume the reactor remains subcritical.)
A. The count rate will rapidly increase (Prompt jump) then gradually increase to a stable value.
B. The count rate will rapidly increase (Prompt jump) then gradually decrease to the previous value.
C. The count rate will rapidly increase (Prompt jump) to a stable value.
D. There will be no change in count rate until criticality is achieved.
ANSWER: A.
Comment: The question suffers from poor terminology. The final count rate is a condition of "equilibrium source multiplication."
QID: B366 (P2265) TOPIC: 292008 KNOWLEDGE: K1.04 [3.3/3.4]
During a reactor startup, source range monitors (SRMs) indicate 100 cps, and Keff is 0.95. After a number of rods have been withdrawn, SRMs indicate 270 cps. Which one of the following is the new Keff? (Assume reactor period is infinity before and after the rod withdrawal.)
A. 0.936
B. 0.971
C. 0.982
D. 0.990
ANSWER: C.
Comment: This question suffers the same defect as B1964. The reactor period is "infinite seconds."
QID: B865 (TOPIC: 292008 KNOWLEDGE: K1.04 [3.3/3.4])
During reactor startup, critical rod position is affected by:
A. core flow rate.
B. source range initial count rate.
C. recirculation ratio.
D. core age.
ANSWER: D.
Comment: The question suffers the same defect as B66. The wording is unsatisfactory.
QID: B966 (TOPIC: 292008 KNOWLEDGE: K1.04 [3.3/3.4])
During an initial reactor fuel load, the 1/M factor decreases from 1.0 to 0.5 after the first 100 fuel assemblies are loaded. What is the current value of Keff?
A. 0.2
B. 0.5
C. 0.875
D. 1.0
ANSWER: B.
Comment: The wording of this question leaves a lot to be desired. Does the 1/M factor actually decrease from 1.0 to 0.5 after 100 fuel assemblies are loaded, or does the decrease occur as the individual assemblies are loaded? See question B1967.
QID: B1067 (P1972) (TOPIC: 292008 KNOWLEDGE: K1.04 [3.3/3.4])
At one point during a reactor plant startup and approach to criticality, count rate is noted to be 780 cps, and Keff is calculated to be 0.92. Later in the same startup, count rate is 4160 cps. What is the new Keff?
A. 0.945
B. 0.950
C. 0.975
D. 0.985
ANSWER: D.
Comment: This question suffers from poor wording. Has anything happened "later" or has time just passed?
QID: B1566 (P266) (TOPIC: 292008 KNOWLEDGE: K1.04 [3.3/3.4])
During a reactor startup, the operator adds 1.0% delta-K/K of positive reactivity by withdrawing control rods, thereby increasing equilibrium source range neutron level from 220 cps to 440 cps. Approximately how much additional positive reactivity is required to raise the equilibrium source range neutron level to 880 cps?
A. 4.0% delta-K/K
B. 2.0% delta-K/K
C. 1.0% delta-K/K
D. 0.5% delta-K/K
ANSWER: D.
Comment: This question suffers the same defect as B1065. Reactivity is not added. In addition, the four choices are incorrectly indicated to represent reactivity.
QID: B2167 (P1867) (TOPIC: 292008 KNOWLEDGE: K1.04 [3.3/3.4])
During a reactor startup, the first reactivity addition caused the count rate to increase from 20 to 40 cps. The second reactivity addition caused the count rate to increase from 40 to 80 cps. Assume keff was 0.92 prior to the first reactivity addition. Which one of the following statements describes the magnitude of the reactivity additions?
A. The first reactivity addition was approximately twice as large as the second.
B. The second reactivity addition was approximately twice as large as the first.
C. The first and second reactivity additions were approximately the same.
D. There is not enough data given to determine the relationship between reactivity values.
ANSWER: A.
Comment: This question suffers the same defect as B1065. Reactivity is not added.
QID: B2266 (TOPIC: 292008 KNOWLEDGE: K1.04 [3.3/3.4])
As a reactor approaches criticality during a reactor startup it takes longer to reach an equilibrium neutron count rate after each control rod withdrawal due to the increased:
A. length of time required to complete a neutron generation.
B. number of neutron generations required to reach a stable neutron level.
C. length of time from neutron birth to absorption.
D. fraction of delayed neutrons being produced as criticality is approached.
ANSWER: B.
Comment: The question suffers the same defect as B67. Use of the primitive life cycle model for explanation is unnecessary and inapproprate.
QID: B2366 (P2367) (TOPIC: 292008 KNOWLEDGE: K1.04 [3.3/3.4])
Refer to the drawing of three 1/M plots (see figure below). A core refueling is in progress with an installed neutron source. During the early stages of the refueling, reactor criticality would be predicted earliest by curve ______ and could possibly be the result of using nuclear instrumentation that is located too ______ the neutron source.
A. A; far from
B. A; close to
C. C; far from
D. C; close to
Comment: This question is technically incorrect because the shape of Curve A, which is representative of BWR loading curves, is due to the fact that the initial fuel assemblies loaded cause a greater change in keff than do late assemblies. The 1/M curve is linear only when plotted against keff.
QID: B2765 (P2766) (TOPIC: 292008 KNOWLEDGE: K1.04 [3.3/3.4])
During a reactor startup, source range indication is stable at 120 cps with Keff at 0.95. After a period of control rod withdrawal, source range indication stabilizes at 600 cps. Which one of the following is the approximate new Keff?
A. 0.96
B. 0.97
C. 0.98
D. 0.99
ANSWER: D.
Comment: This question suffers poor terminology. Restate as, After several control rod withdrawal increments, ... . Use of "period" can be confused with reactor rate.
QID: B2966 (P2968) (TOPIC: 292008 KNOWLEDGE: K1.04 [3.3/3.4])
A reactor startup is in progress; control rod withdrawal has just been stopped to assess criticality. Which one of the following is a combination of indications in which each listed indication supports a declaration that the reactor is critical?
A. Period stabilizes at +200 sec; source range count rate is slowly increasing; inverse multiplication (1/M) value equals 0.000.
B. Period is approaching infinity; source range count rate increases and then stabilizes; inverse multiplication (1/M) value equals 0.111.
C. Period stabilizes at +200 sec; source range count rate is slowly increasing; inverse multiplication (1/M) value equals 1.000.
D. Period is approaching infinity; source range count rate increases and then stabilizes; inverse multiplication (1/M) value equals 1.111.
ANSWER: A.
Comment: This question is technically incorrect because the mathematical representation of inverse multiplication is valid only for keff < 1.0.
. QID: B267 (TOPIC: 292008 KNOWLEDGE: K1.05 [4.3/4.3])
A reactor startup is in progress with Keff at 0.995 and stable source range indication. If Keff is increased to 0.997 by control rod withdrawal, reactor period will initially become ____________ and then ____________.
A. positive; approach infinity
B. positive; stabilize at a positive value
C. negative; approach infinity
D. negative; stabilize at a negative value
ANSWER: A.
Comment: This question suffers the same defect as B1964. The final reactor period is "infinite seconds."
QID: B1365 (P267) (TOPIC: 292008 KNOWLEDGE: K1.05 [4.3/4.3])
As criticality is approached during a reactor startup, equal insertions of positive reactivity result in a ____________ change in equilibrium count rate and a ____________ time to reach each new equilibrium.
A. larger; longer
B. larger; shorter
C. smaller; longer
D. smaller; shorter
ANSWER: A.
Comment: This question suffers the same defect as B266. Reactivity is not added.
QID: B1267 (TOPIC: 292008 KNOWLEDGE: K1.06 [4.2/4.2])
A reactor is exactly critical during a reactor startup. Which one of the following must be closely monitored and controlled to ensure safe operation of the reactor as power is raised to the point of adding heat?
A. Reactor period
B. Reactor temperature
C. Source range count rate
D. Power peaking factors
ANSWER: A.
Comment: The question is technically incorrect because of improper terminology, namely "exactly" critical. Criticality is a unique condition that does not require qualification.
QID: B123 (P68) (TOPIC: 292008 KNOWLEDGE: K1.07 [3.9/3.9])
With Keff = 0.985, how much reactivity must be added to make a reactor critical?
A. 0.0148 delta-K/K
B. 0.0150 delta-K/K
C. 0.0152 delta-K/K
D. 0.0154 delta-K/K
ANSWER: C.
Comment: This question suffers the same defect as B1065. Reactivity is not added and the four choices are incorrectly indicated to represent reactivity.
QID: B667 (TOPIC: 292008 KNOWLEDGE: K1.07 [3.9/3.9])
When a reactor is exactly critical, reactivity is:
A. greater than 1.0% delta-K/K.
B. equal to 1.0% delta-K/K.
C less than 1.0% delta-K/K.
D. undefined.
ANSWER: C.
Comment: This question suffers the same defect as B1267. Criticality is an exact condition.
QID: B867 (P2267) (TOPIC: 292008 KNOWLEDGE: K1.07 [3.9/3.9])
When a reactor is exactly critical, reactivity is:
A. infinity.
B. undefined.
C. 0.0 delta-K/K.
D. 1.0 delta-K/K.
ANSWER: C.
Comment: This question suffers the same defect as B1267. Criticality is an exact condition.
QID: B68 (P1967) (TOPIC: 292008 KNOWLEDGE: K1.08 [4.1/4.1])
Assume a reactor is critical at a power level below the point of adding heat. For a 0.01% delta-K/K positive reactivity addition, the reactor period will be:
A. shorter at a higher reactor coolant temperature.
B. longer at a higher reactor coolant temperature.
C. shorter at the end of core life (EOL) than at the beginning of core life (BOL).
D. longer at EOL than at BOL.
ANSWER: C.
Comment: This question suffers the same defect as B1566. Reactivity is not added and the indication that the 0.01% represents reactivity is incorrect.
QID: B1069 (TOPIC: 292008 KNOWLEDGE: K1.08 [4.1/4.1])
A reactor is critical just below the point of adding heat (POAH) at a temperature of 160 F. Which one of the following will result in reactor power increasing and stabilizing at the POAH? (Assume a negative moderator temperature coefficient.)
A. Reactor recirculation flow increases 10%.
B. Reactor coolant temperature increases 3 F.
C. A single control rod moves in one notch.
D. Core xenon-135 concentration decreases.
ANSWER: D.
Comment: The question is technically incorrect because reactor power will seek criticality at a level where the heating rate introduces negative reactivity change at the same rate that xenon decay is introducing positive reactivity change. The power level will be greater than the POAH.
QID: B2668 (P2667) (TOPIC: 292008 KNOWLEDGE: K1.08 [4.1/4.1])
A reactor is critical at 10-6% power. Control rods are withdrawn for 2 seconds and then stopped, resulting in a stable reactor period of positive 100 seconds. If control rods were inserted (instead of withdrawn) for 2 seconds with the reactor initially critical at 10-6 % power, the stable reactor period would have been: (Assume equal absolute values of reactivity are added in both cases.)
A. shorter than negative 100 seconds, because reactor power decreases result in smaller delayed neutron fractions.
B. shorter than negative 100 seconds, because reactor power decreases are less limited by delayed neutrons.
C. longer than negative 100 seconds, because reactor power decreases result in larger delayed neutron fractions.
D. longer than negative 100 seconds, because reactor power decreases are more limited by delayed neutrons.
ANSWER: D.
Comment: The question is technically incorrect because there are two correct answers. Choice C is correct because the delayed neutron population fraction, represented by (beta - rho), increases with power decrease caused by negative reactivity. Both Choice C and Choice D are contributing to a longer stable rate.
QID: B669 (TOPIC: 292008 KNOWLEDGE: K1.10 [3.6/3.6])
A reactor is being started up with a stable positive 100-second period and power is entering the intermediate range (below the point of adding heat). Assuming no operator action, which one of the following describes the response of reactor period?
A. The heat produced by the reactor through all ranges of the intermediate range indication, is insufficient to raise the fuel or moderator temperatures, and reactor period remains constant throughout the intermediate range.
B. As heat production in the reactor exceeds ambient losses, the temperature of the fuel and moderator will increase, adding negative reactivity, and reactor period will become infinite.
C. As heat production in the reactor exceeds ambient losses, positive reactivity added by the fuel temperature increase counteracts the negative reactivity added by the moderator temperature increase, and reactor period remains constant throughout the intermediate range.
D. Prior to reaching the point of adding heat, the fuel temperature increase will add negative reactivity and reactor period will approach infinity.
ANSWER: B.
Comment: This question suffers the same defects as B1065 and B1964. Reactivity is not added and the reactor period will become "infinite seconds." In addition, the initial conditions which determine the response should be specified in the question, not in the answer. Ambient heat losses are an initial condition.
QID: B133 (P1169) (TOPIC: 292008 KNOWLEDGE: K1.12 [3.6/3.7])
A reactor is critical well below the point of adding heat when a small amount of positive reactivity is added to the core. If the same amount of negative reactivity is added to the core approximately 1 minute later, reactor power will stabilize at:
A. the initial power level.
B. somewhat higher than the initial power level.
C. somewhat lower than the initial power level.
D. the subcritical multiplication equilibrium level.
ANSWER: B.
Comment: This question suffers the same defect as B1065. Reactivity is not added. In addition, the wording, "power will stabilize" is poor. The reactor will be "critical" at a power level somewhat higher ...
QID: B2467 (TOPIC: 292008 KNOWLEDGE: K1.12 [3.6/3.7])
Criticality has just been achieved during a reactor startup at 160 F. The operator withdraws control rods as necessary to establish a stable positive 30-second reactor period. No additional operator actions are taken. How will reactor period and reactor power respond? (Assume a negative moderator temperature coefficient.)
A. Reactor power will increase and stabilize at the POAH; reactor period will remain constant until the POAH is reached and then stabilize at infinity.
B. Reactor power will increase and stabilize at the POAH; reactor period will decrease slowly until the POAH is reached and then stabilize at infinity.
C. Reactor power will increase and stabilize above the POAH; reactor period will remain constant until the POAH is reached and then stabilize at infinity.
D. Reactor power will increase and stabilize above the POAH; reactor period will decrease slowly until the POAH is reached and then stabilize at infinity.
ANSWER: A.
Comment: This question suffers the same defect as B1964. Reactor period will stabilize at "infinite seconds." In addition, the question is technically incorrect because the initial conditions are not specified. The power will not level off unless ambient heat loss or steam demand is of the order of at least 0.5% of rated power.
QID: B1467 (P2269) (TOPIC: 292008 KNOWLEDGE: K1.12 [3.6/3.7])
A reactor is critical at the point of adding heat when a small amount of negative reactivity is added to the core. If the same amount of positive reactivity is added to the core approximately 5 minutes later, reactor power will:
A. stabilize at the subcritical multiplication equilibrium neutron level.
B. stabilize at a level lower than the initial power level.
C. continue to decrease on a negative 80 second period.
D. stabilize at the initial power level.
ANSWER: B.
Comment: This question suffers the same defect as B1065. Reactivity is not added. In addition, the wording, "power will stabilize" is poor. The reactor will be "critical" at a power level somewhat lower ... Choice B is not necessarily correct if there are heat losses or xenon decay.
QID: B2568 (P2568) (TOPIC: 292008 KNOWLEDGE: K1.12 [3.6/3.7])
A reactor is currently at 10-3% power with a positive 60 second reactor period. An amount of negative reactivity is added to the core that places the reactor on a negative 40 second reactor period. If the same amount of positive reactivity is added to the core approximately 5 minutes later, reactor power will:
A. increase and stabilize at the point of adding heat.
B. increase and stabilize at 10-3% power.
C. continue to decrease on a negative 40 second period until the equilibrium source neutron level is reached.
D. continue to decrease with an unknown period until the equilibrium source neutron level is reached.
ANSWER: A.
Comment: This question suffers the same defect as B1065. In addition, the question is technically incorrect because the initial conditions are not specified. The power will not level off unless ambient heat loss or steam demand is of the order of at least 0.5% of rated power.
QID: B670 (P670) (TOPIC: 292008 KNOWLEDGE: K1.13)
After taking critical data during a reactor startup, the operator establishes a 26-second reactor period to increase power to the point of adding heat (POAH). How much negative reactivity feedback must be added at the POAH to stop the power increase?
Assume:
ß = 0.00579
l* = 1 x 10-5 seconds
lambdaeff = 0.1 seconds-1
A. 0.16% delta-K/K
B. 0.19% delta-K/K
C. 0.23% delta-K/K
D. 0.29% delta-K/K
ANSWER: A.
Comment: This question suffers the same defect as B1566. Reactivity is not added and the four choices are incorrectly indicated to represent reactivity. In addition this question is technically incorrect because the amount of negative reactivity feedback to "stop" the power increase occurs at power turning and is less than the amount of negative reactivity feedback required to establish criticality.
QID: B968 (TOPIC: 292008 KNOWLEDGE: K1.13 [3.8/3.9])
After taking critical data during a reactor startup, the operator establishes a positive 26-second reactor period to increase power to the point of adding heat (POAH). How much negative reactivity must be added to stabilize power at the POAH? (Assume ßeff = 0.00579.)
A. 0.10% delta-K/K
B. 0.16% delata-K/K
C. 1.0% delta-K/K
D. 1.6% deltaK/K
ANSWER: B.
Comment: This question suffers the same defect as B1566. Reactivity is not added and the four choices are incorrectly indicated to represent reactivity. In addition this question is technically incorrect because the initial conditions necessary to establish constant power at the POAH are not specified as existing.
QID: B1667 (TOPIC: 292008 KNOWLEDGE: K1.13 [3.8/3.9])
After taking critical data during a reactor startup, the operator establishes a 38 second reactor period to increase power to the point of adding heat (POAH). Which one of the following is the approximate negative reactivity required to stop the power increase at the POAH? (Assume that ß = 0.00579.)
A. 0.01% delta-K/K
B. 0.12% delta-K/K
C. 0.16% delta-K/K
D. 0.21% delta-K/K
ANSWER: B.
Comment: This question suffers the same defect as B670. Reactivity is not added and the four choices are incorrectly indicated to represent reactivity. The power increase is "stopped" at the point of power turning.
QID: B1769 (TOPIC: 292008 KNOWLEDGE: K1.13 [3.8/3.9])
After taking critical data during a reactor startup, the operator establishes a positive 31-second reactor period to increase power to the point of adding heat (POAH). Which one of the following is the appropriate amount of reactivity needed to stabilize power at the POAH? (Assume ßeff = 0.00579.)
A. -0.14% delta-K/K
B. -0.16% delta-K/K
C. -1.4% delta-K/K
D. -1.6% delta-K/K
ANSWER: A.
Comment: This question suffers the same defect as B968. Reactivity is not added and the four choices are incorrectly indicated to represent reactivity.